Mechanics of Advanced Composite StructuresMechanics of Advanced Composite Structures
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Feed provided by Mechanics of Advanced Composite Structures. Click to visit.Elasto-thermodiffusive Response in a Two Dimensional Transversely Isotropic Medium
http://macs.journals.semnan.ac.ir/article_3289_0.html
The present article deals with the investigation of elasto-thermodiffusive interactions in a transversely isotropic elastic medium in the context of thermoelasticity with one relaxation time and two relaxation time parameters respecytively. The resulting non-dimensional coupled equations are applied to a specific problem of a half-space in which the surface is free of tractions and is subjected to time-dependent thermal loading and chemical loadings. The analytical expressions for the displacement components, stresses, temperature, strain, mass diffusion and the chemical potential are obtained in the physical domain by employing the normal mode analysis as a tool. These expressions are also calculated for a copper-like material and have been depicted graphically. A comparative study of diffusive medium and thermoelastic medium is carried out and it was seen that the effect of diffusion is significant on the thermophysical quantities. Further, it is also observed that in absence of the effect of thermodiffusion, the results agree with the results of existing literature.Sat, 22 Sep 2018 20:30:00 +0100The Effect of Temperature Dependency on the Thermo-Electro-Elastic Analysis of Functionally ...
http://macs.journals.semnan.ac.ir/article_3781_455.html
Results of electro-thermo-elastic analysis of a functionally graded thick-walled spherical shell made of temperature dependent materials are presented in this article. All material properties are assumed temperature-dependent and also are graded along the thickness direction based on power function. Temperature dependency is accounted for all material properties including, thermal, mechanical and electrical properties based on linear variation. Thermal conduction relation is solved using thermal boundary conditions at inner and outer radii for temperature dependent and independent cases. Substitution of temperature distribution into constitutive relations and then into equilibrium and Maxwell equations would give final governing equations having variable thickness. The variable coefficient governing equations are solved using the division method. The numerical results are presented for both temperature-dependent and temperature-independent cases so as to investigate the effect of temperature dependencies. The results indicate that considering temperature dependency would lead to significant changes in responses including radial and circumferential displacements and stresses, electric potential and temperature distribution.Sun, 31 Mar 2019 19:30:00 +0100Fluid-Structure Interaction of Vibrating Composite Piezoelectric Plates using exponential shear ...
http://macs.journals.semnan.ac.ir/article_3645_0.html
In this paper fluid-structure interaction of vibrating composite piezoelectric plates is investigated. Since the plate is assumed to be moderately thick, rotary inertia effects and transverse shear deformation effects are considered by using exponential shear deformation theory. Fluid velocity potential is obtained using the Laplace equation and fluid boundary conditions and wet dynamic modal functions of the plate are expanded in terms of finite Fourier series to satisfy compatibility along the interface between plate and fluid. The electric potential is assumed to have a cosine distribution along the thickness of the plate in order to satisfy the Maxwell equation. After deriving the governing equations using Hamilton’s principle, the natural frequencies of the fluid-structure system with simply supported boundary condition are calculated using the Galerkin method. The model is compared with the available results in the literature and then the effects of different variables such as depth of fluid, the width of fluid, plate thickness and aspect ratio on natural frequencies and mode shapes are illustrated.Thu, 24 Jan 2019 20:30:00 +0100Delamination Analysis in Composite Root of a Carbon-Layer Reinforced Wind Turbine Blade
http://macs.journals.semnan.ac.ir/article_3795_455.html
The inconsistencies accompanied with material properties tipically cause the rise of delamination risk in composites made of different types of glass and crabon fibers. In this study, the delamination of a composite beam reinforced with a carbon layer under bending load is investigated. To this end, a small piece of a wind turbine blade root in the form of a heterogeneous laminated plate is simulated and analyzed. The methodology consists of two parallel approaches, including the experimental measurements and computer simulations. In the experimental program, the delamination of different specimens has been examined by three-point bending (3PB) tests. The diagrams of load versus load line displacement are recorded. In computer simulation, the geometry of composite laminate is re-modeled and stress analysis is performed. The results confirm that delamination loads obtained from the simulations are reliable and in good agreement with those obtained from the experimental procedures. The results of experimental measurements and computational simulations are utilized to predict the delamination failure and to optimize the lay-up sequence of the reinforced structure.Sun, 31 Mar 2019 19:30:00 +0100Investigation of hardness, morphology and structural analysis of NiCrBSi composite coating on ...
http://macs.journals.semnan.ac.ir/article_3625_0.html
High velocity oxyfuel (HVOF) is one of the emerging technologies among the thermal spraying techniques, for producing uniform and dense coatings, having high hardness and very low porosity. A NiCrBSi alloy coating was prepared with approximately 400µm thick, on the A516 steel by means of HVOF and analyzed with regard to its detailed microstructures, phase formation, thickness, roughness and microhardness. The obtained coating was crack free, mecanically bonded to the substrate and had very low porosity. A microhardness tester was used in order to determine the mechanical properties of the coating. The microstructure of the coating and its phase trans-formations was characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS) respectively. The major crystalline phases involve Cr3NiB6, Ni31Si12, Ni4B3, Ni3B compounds and Ni-γ solid solution. Also amorphous phase were obtained in the coating. The results showed that coating microhardness values were in the range of 700-800 Hv and a uniform distribution of different elements have been observed.Sun, 03 Feb 2019 20:30:00 +0100Health Monitoring for Composite under Low-Cycle Cyclic Loading, Considering Effects of Acoustic ...
http://macs.journals.semnan.ac.ir/article_3782_455.html
Composites have been widely used in the aerospace industry. Due to the requirement of a high safety for such structures, they could be considered for health monitoring. The acoustic emission approach is one of most effective methods for identifying damages in composites. In this article, standard specimens were made from carbon fibers and the epoxy resin, with the [03/902/02]s layout. Then, samples were subjected to low-cycle cyclic loading. Besides, signals were recorded with two types of acoustic emission sensors. Obtained results indicated that by increasing the number of cycles and approaching the final lifetime of the sample, the cumulative energy of signals increased. The fracture surface of specimens was analyzed using the scanning electron microscopy. As a consequent and a general conclusion, based on obtained results, it could be claimed that both wide-band and mid-band acoustic emission sensors could be effectively utilized for detecting the defects in composite structures.Sun, 31 Mar 2019 19:30:00 +0100Analytical Approach for Thermo-electro-mechanical Vibration of Piezoelectric Nanoplates Resting ...
http://macs.journals.semnan.ac.ir/article_3646_0.html
In the present work thermo-electro vibration of the piezoelectric nanoplates resting on the elastic foundations using nonlocal elasticity theory are considered. In-plane and transverse displacements of the nanoplate are approximated by six different modified shear deformation plate theories by considering transverse shear deformation effects and rotary inertia. Moreover, two new distribution of transverse shear stress along the thickness of the nanoplate are introduced for the first time. The equations of motion are derived by implementing Hamilton’s principle and solved using analytical method for various boundary conditions including SSSS, CSSS, CSCS, CCSS and CCCC. Based on a comparison with the previously published results, the accuracy of the results is shown. Finally, the effects of different parameters such as boundary conditions, variations of the thickness to length ratio, aspect ratio, increasing temperature, external voltage, foundation coefficients and length scale on the natural frequency of the plate are shown and discussed in detail.Sun, 03 Feb 2019 20:30:00 +0100Nonlinear Vibration Analysis of the Composite Cable using Perturbation Method and the ...
http://macs.journals.semnan.ac.ir/article_3792_455.html
In this study, nonlinear vibration of a composite cable is investigated by considering nonlinear stress-strain relations. The composite cable is composed of an aluminum wire as reinforcement and a rubber coating as matrix. The nonlinear governing equations of motion are derived about to an initial curve and based on the fundamentals of continuum mechanics and the nonlinear Green-Lagrangian strain, using the Hamilton's principle. The equations of motion of the system are reduced into the ordinary differential equations using the Galerkin method, and solved by the perturbation method (multiple scales). Time-response diagrams are presented for the composite cable with different volume fractions of the matrix and the reinforcement. It is predicted that the more volume fraction of the matrix is, the more nonlinear quadratic and cubic terms in the governing equations of motion affects the vibration of the cable. Results indicate that increasing the length of the cable would decrease the amplitude of the time response of the system.Sun, 31 Mar 2019 19:30:00 +0100Influence of Different Foaming Conditions on the Mechanical, Physical, and Structural ...
http://macs.journals.semnan.ac.ir/article_3757_0.html
In this paper, the effects of different foam production times and temperatures on the mechanical, physical, and structural properties of polypropylene (PP) foam were investigated. The microcellular PP foams were carried out using supercritical carbon dioxide (sc-CO2) as a physical foaming agent in a batch process. The samples were placed in a pressure vessel and were saturated with sc-CO2 at room temperature (23- 25°C) and saturation pressure of 40 MPa for 35 hours. Then, samples were removed from the vessel after releasing the pressure and were immersed in a glycerin bath for different times of 90, 180, and 270 seconds and different temperatures of 155°C, 165°C, and 175°C. The mechanical responses of samples, e.g., flexural, Izod impact, and Dynamic Mechanical Thermal properties, and physical characterization containing water absorption and relative density were studied. Scanning Electron Microscopy (SEM) was applied to investigate the surface morphology. The cell size, cell density, and cell structure of PP foams were studied by morphological parameters. X-ray diffractometer was used to investigate the interaction effect on the samples. Results showed that in the semi-crystalline polymers such as polypropylene, the foaming temperature must be higher than the melting temperature of PP. A simultaneous examination of mechanical, physical, morphological test results as well as cell structure properties shows that the best temperature and time conditions for producing PP foams are the temperature of 175°C and time of 270 seconds, respectively. These optimum conditions can be used in the industrial production of PP foams.Sun, 14 Apr 2019 19:30:00 +0100Crushing Analysis of Empty and Foam-Filled Cylindrical and Conical Corrugated Composite Tubes
http://macs.journals.semnan.ac.ir/article_3793_455.html
In the present article, a numerical study is performed to investigate the crushing behavior of cylindrical and conical corrugated composite tubes. Different aluminum foams are applied to the proposed structures in order to offer an excellent energy absorption capacity. The crushing behavior of tubes are evaluated in terms of two parameters: SEA (specific energy absorption) and CFE (crush force efficiently). So, in order to study the effect of corrugation on the crashworthiness of composite tubes, a comprehensive numerical analysis of corrugated carbon/BMI tubes is performed under axial loadings. The effect of geometric parameters of corrugation including number and radius of corrugations is studied by FE simulation of several models in LS-DYNA. Comparison between corrugated tubes and straight one demonstrated that the CFE would be improved significantly in these new models. Furthermore, the absorbed energy increased by using foams. SEA, mean force and peak forces increased by increasing the foam density while the crush force efficiently decreased considerably due to the fact that in higher densities, densification region accrues in fewer strains.Sun, 31 Mar 2019 19:30:00 +0100Discrepancies between free vibration of FML and composite cylindrical shells reinforced by CNTs
http://macs.journals.semnan.ac.ir/article_3773_0.html
In this study, discrepancies between the free vibration of fiber-metal laminate (FML) and composite cylindrical shells based on Love’s first approximation shell theory reinforced by carbon nanotubes (CNTs) have been considered by beam modal function model. The representative volume elements are consisting of three and four phases for composite and FML structures, respectively, which are included fiber, CNTs, polymer matrix and metal for FML cylindrical shells and the metal section is ignored for composite cylindrical shells. The modulus of carbon nanotubes reinforced composites cylindrical shell can be defined based on rule of mixture. In addition, the fiber phase can be reinforced by the obtained matrix by extended rule of mixture. The frequencies of FML and composite cylindrical shells reinforced by CNTs have been compared to each other for different materials, lay-ups, boundary conditions, axial and circumferential wave numbers. The results show that the frequencies of CNTFPML are more than the CNTFP for n=1, but with increasing the n this procedure is converted.Wed, 24 Apr 2019 19:30:00 +0100Propagation of Matrix Cracking and Induced Delaminatin in Cross-Ply Composite Beams Subjected ...
http://macs.journals.semnan.ac.ir/article_3791_455.html
Due to the mismatch of mechanical properties in composite laminates, propagation of delami-nation is considered as a severe damage mechanism in beams with various lay-up configurations. Delamination can be generated due to matrix cracking propagation or it can also be initiated due to the manufacturing process before using composite beams. Using a micromechanics model, this study is aimed to investigate the bending moment required for matrix cracking and induced delamination in cross-ply composite beams. To that end, a unit cell is selected from the lamina surface in a composite beam containing matrix cracking and delamination. Later, the governing equation of stress and displacement fields are extracted in the unit cell to calculate the strain energy release rate due to the propagation of matrix cracking and induced delamination. In order to validate this method, the stiffness variations in Carbon-Epoxy cross-ply laminate [90/02]s is examined and the obtained results are compared with the numerical results. It concluded that there is a favorable agreement between the results of the proposed micromechanics model and available numerical results.Sun, 31 Mar 2019 19:30:00 +0100Transient Thermal Stresses Analysis in a FPGM Cylinder
http://macs.journals.semnan.ac.ir/article_3774_0.html
The present study has investigated the analysis of stress, strain, displacement, and electrical po-tential of a thick hollow cylinder made of FGPM under mechanical and thermal loads. Distribution of mechanical property of material is considered along the shell stick through power distribution function. Thermal loads have been taken to signify the difference of temperature between outer and inner surfaces for every type of mechanical property. After extracting and solving differential equations in transient state and the observation of mechanical and thermal boundary conditions, governing functions are obtained through follows parameters: thermal conduction non-homogeneous parameters, thermal linear distribution coefficient, elastic stiffness constant, piezo-electric coefficient, and dielectric constants. By increasing the radius, the value of radial dis-placement and temperature increase and the do-main of vibration gets larger. Also, the value of hoop displacement and electrical potential in-crease and the value of radial and shear stresses decrease, and the domain of vibration gets smallerWed, 24 Apr 2019 19:30:00 +0100Effects of Magnetic Field in Creep Behavior of Three-Phase Laminated Composite Cylindrical Shells
http://macs.journals.semnan.ac.ir/article_3788_455.html
Due to the importance effect of magnetic field on the history of long-term radial and circumfer-ential creep strain and radial displacement for a three-phase nano-composite exposed to an internal pressure and placed uniform temperature, the present article subject has been pro-posed. Three-phase nano-composite made of single-walled carbon nano tubes (SWCNTs)/ glass fiber (GF)/vinylester used to micromechanical models in order to calculate the mechanical and thermal properties. By assuming non-linear viscoelastic based on Schapery integral model and using classical laminate theory, Prandtl-Reuss relations and Mendelson’s approximation meth-od achieved results. Distribution of the radial creep strain, circumferential creep strain and radial displacement in two states including without and with magnetic field and three tempera-ture conditions for laminated lay-ups [0/45/0/45] described for 10 years. The results indicate that the magnetic field has reduced the radial and circumferential creep strain and radial dis-placement. Furthermore, the temperature increase in the magnetic field is less effective on the increased values of creep strain and radial displacement. Finally, It has been founded that mag-netic field would reduce the creep strain of all case studies.Sun, 31 Mar 2019 19:30:00 +0100Sintered Steel Composites Reinforced with Ceramic Nanoparticles: Fabrication, Characteristics ...
http://macs.journals.semnan.ac.ir/article_3775_0.html
Steel composites reinforced with alumina nanoparticles were prepared by powder metallurgy process. Samples containing two different amounts of carbon (0.35 and 0.55 wt.%) and 0-5 wt.% Al2O3 nanoparticles were fabricated by mixing, compacting and sintering of diffusion bonded Distaloy AE powder. The density, hardness and wear tests were performed on prepared samples. Furthermore, the microstructures and worn surfaces analyzed by optical and scanning electron microscope (SEM), respectively. The wear tests were carried out in forces of 30, 40 and 50 KN and 1000 m distance in dry condition and ambient temperature. The results shown that the increasing of alumina nanoparticles reduces the density (~ 10.8 and 9.6 % for 0.35 and 0.55 wt.% C, respectively) and increases the hardness (~ 14.1 and 7.2 % for 0.35 and 0.55 wt.% C, respectively) of sintered samples. With increasing carbon content, the amount of lost material and the rate of wear decrease. The lost volume increases with increasing wear distance and applied force. Addition of reinforcement to the steel matrix, improves wear resistance up to 3 wt.% alumina nanoparticles. This increase in the samples varies between ~ 30 to 73%. More increasing of alumina (5 wt.%) decreases the wear resistant of samples. The wear mechanisms including oxidation in low forces that convert to adhesive and abrasive with increasing applied force. The wear curves indicate that as the wear distance increases, the lost volume increases, while the wear rate decreases.Wed, 24 Apr 2019 19:30:00 +0100Numerical Crashworthiness Analysis of Graded Layered Foam- Filled Tubes Under Axial Loading
http://macs.journals.semnan.ac.ir/article_3778_455.html
In this article, the results of a study on energy absorption characteristics of foam-filled thin-walled structures with finite element analysis have been presented. Four specimens of thin walled structures have been filled with uniform foam and three specimens have been filled with linear four-layered foam. Also, eight layers HLH (High-Low-High) and eight layers LHL (Low-High-Low) have been simulated. The total weight of all layered specimens is the same and main difference is just the arrangement of the layers. In order to study the energy absorption behavior of the specimens, they have been subjected to quasi-static crushing load. The results indicated that by utilizing the filler foam in the thin-walled energy absorbers, the energy absorption capacity of the foam filled specimens in comparison with hollow specimens, significantly promotes; however, the initial peak force for hollow specimens is lower than the foam-filled specimens. Consequently, from the layered specimens, LHL showed higher specific energy absorption and less initial peak force compared with other specimens, in which the LHL specimen shows 16% more initial peak force and 114% more specific energy absorption than the hollow specimen.Sun, 31 Mar 2019 19:30:00 +0100A New Three-Dimensional Refined Higher-Order Theory for Free Vibration Analysis of Composite ...
http://macs.journals.semnan.ac.ir/article_3776_0.html
A new closed form formulation of three-dimensional (3-D) refined higher-order shell theory (RHOST) to analyze the free vibration of composite circular cylindrical shells is presented. The shell is considered to be laminated with orthotropic layers and simply supported boundary conditions. The proposed theory is used to investigate the effects of the in-plane and rotary inertias as well as transverse normal and shear strains on the dynamic response of thick com-posite cylindrical shells. The trapezoidal shape factor of the shell element is incorporated to obtain accurate stress-resultants. By using Hamilton’s principle, the equations of motions are obtained and solved using the Galerkin method. Numerical results for the natural frequencies are verified by making comparison with the 3-D exact elasticity iterative solutions in the litera-ture. Also, the validity of the results is further verified by ABAQUS commercial code. According to the results, for thick composite cylinders with large length-to-radius and orthotropic ratios, thorough thickness exact integration yields accurate stress-resultants for proper prediction of the natural frequencies.Wed, 24 Apr 2019 19:30:00 +0100Non-Linear Analysis of Functionally Graded Sector Plates with Simply Supported Radial Edges ...
http://macs.journals.semnan.ac.ir/article_3785_455.html
In this study, nonlinear bending of functionally graded (FG) circular sector plates with simply supported radial edges subjected to transverse mechanical loading has been investigated. Based on the first-order shear deformation plate theory with von Karman strain-displacement relations, the nonlinear equilibrium equations of sector plates are obtained. Introducing a stress function and a potential function, the governing equations which are five non-linear coupled equations with total order of ten are reformulated into three uncoupled ones including one linear edge-zone equation and two nonlinear interior equations with total order of ten. The uncoupling makes it possible to present analytical solution for nonlinear behavior of FG sector plates with simply-supported radial edges via perturbation technique and Fourier series method. The material properties are graded through the plate thickness according to a power-law distribution of the volume fraction of the constituents. The results are verified by comparison with the existing ones in the literature. The effects of non-linearity, material constant and boundary conditions on bending of an FG sector plate are studied. It is shown that in bending analysis of functionally graded sector plates, linear theory is solely applicable for w/h and is inadequate for analysis of fully simply supported FG sector plates even in the small deflection range.Sun, 31 Mar 2019 19:30:00 +0100Investigation of Tensile Characteristics of an Epoxy Matrix Composite with Uni-Directional and ...
http://macs.journals.semnan.ac.ir/article_3777_0.html
This paper investigates the usage of natural hemp fibers to reinforce polymer matrix composites. The characteristics are obtained experimentally via tensile test of such composites with unidirectional and hybrid tissue fibers. After preparation of different standard tensile stress test specimens via manual layup, the standard tensile tests are applied to the specimens. Young’s modulus, ultimate tensile stress and the amount of absorbed energy before fracture are obtained through experiments. A comparison is performed with respect to fibers posture. In all the cases, the tissue fiber samples gave a higher strength in comparison with the laminated fibers. The main reason is the effect of cloth tissue and orthogonal arrangement of the fibers. In the laminated specimens, the fibers are effective only in tensile direction but in the tissue specimens, the tensile direction fibers are more reinforced because they are woven with perpendicular fibers that leads to increase the strength of the composite.Wed, 24 Apr 2019 19:30:00 +0100Nonlocal analysis of longitudinal dynamic behavior of nanobars with surface energy effect
http://macs.journals.semnan.ac.ir/article_3779_0.html
Due to considerable stored energy in surfaces of nano-scales in comparison with the stored energy in their bulk, considering the surface energy is necessary for analysis of various behaviors of nano-scales for more precise design and manufacturing of them. In this paper, the longitudinal dynamic behavior of nanobars in the presence of the surface energy parameters is studied. To this end, the longitudinal dynamic behavior of nanobars is modeled based on the simple theory. To consider the effects of the surface energy parameters the surface elasticity theory is used. In addition, the nonlocal elasticity theory is implemented to capture the size effect. Then, the governing equation of motion and corresponding boundary conditions are derived from Hamilton’s principle. The governing equation becomes inhomogeneous due to considering the surface energy parameters while in none of the previous researches like the investigation of transverse vibration of nanobeams and torsional vibration of nanobars, the surface energy parameters do not cause inhomogeneity of the governing equation. Due to inhomogeneity of the governing equation, the homogeneous case is firstly solved, and frequencies and mode shapes of nanobar are obtained for fixed-fixed and fixed-free boundary conditions. Then, by using the modal analysis method and Duhamel’s integral, the inhomogeneous governing equation of motion is solved and the overall dynamic response of nanobar is reported.Wed, 24 Apr 2019 19:30:00 +0100Improving the performance of the sandwich panel with the corrugated core filled with metal ...
http://macs.journals.semnan.ac.ir/article_3780_0.html
A new type of composite structure with a metal foam is reinforced by the metal corrugated core, which called metal-foam-filled sandwich panels with a corrugated or V-frame core, is modelled, simulated, and studied in this paper. All types of samples with different relative densities of the foam are tested and analysed under the drop hammer load. The sandwich panel included two aluminium face-sheet, aluminium foams, and aluminium corrugated or V-frame cores. Mathematical and finite element models were also developed to predict the ef-fects of the relative density of the foam and other geometric parameters on the energy absorp-tion. In addition, we derived the mathematical equations based on a mass-spring-damper problem with two degree-of-freedom (DOF) to evaluate the kinetic and kinematic parameters of the sandwich panel, such as velocity, acceleration, contact force, and energy absorption. It was found that the models could represent the dynamic response of the sandwich panel. Fi-nally, to improve the performance of the sandwich panel, we used an optimization method to find the optimum parameters which play an important role.Wed, 24 Apr 2019 19:30:00 +0100The Role of Natural additives on the Wear and Friction Properties of Nanocomposites for ...
http://macs.journals.semnan.ac.ir/article_3783_0.html
For several years, asbestos was used as a friction ingredient of friction materials; but because of its hazardous effects on human health, the enforced regulation restricted its application. So, several attempts were made to replace the alternative potential materials with eco- friendly behaviors. In the present study, the effect of banana peel and bagasse particle additives on the friction and wear behaviour of multi- ingredient friction material composites was investigat-ed. In order to develope an optimized properties of friction nanocomposite, the type and con-tent of natural additives were changed beside the constant amount of other constituent such as alumina nanoparticle and other functional ingredient. The microstructural investigation and wear test were performed. The results showed, as the natural additives content increase the density of composite and the hardness decrease. The highest hardness and friction values and the lowest specific wear rate achieve for a composite sample with 5 wt. % of baggase addi-tive.Wed, 24 Apr 2019 19:30:00 +0100Effect of aging on fracture toughness of Al6061-Graphite particulate composites
http://macs.journals.semnan.ac.ir/article_3784_0.html
This paper exhibits the investigative work conducted on the fracture toughness and microstructure of Al6061-graphite particulate composites. The requisite specimens were prepared using stir casting technique. The casting is carried out for 9% by weight fractions of graphite particles. The specimens considered to evaluate the fracture toughness are compact tension specimens. The Al6061-9%graphite particulate Metal matrix composites has been heated to a temperature 530±5 ºC for 2 hours followed by quenching in water. Artificial aging was done at 155°C, for periods ranging from 00 to 7 hours and subsequently cooled in the air. Fracture toughness investigations were carried out on Al6061-9%graphite by using compact tension (CT) specimens. It is observed from the results that as aging time increases the fracture toughness increases. This gain in fracture toughness is with the loss of ductility. Examination of the fractured surface of Al6061-graphite is done using a scanning electron microscope (SEM) which shows the brittle fracture of the composite.Wed, 24 Apr 2019 19:30:00 +0100Thermoelastic Analysis of Compressor’s Spool in Turbojet Engine and Redesign It Using ...
http://macs.journals.semnan.ac.ir/article_3786_0.html
In this paper, an exact analysis of compressor’s spool in a turbojet engine has been investigat-ed. The spool is modeled as a rotating thick-walled hollow circular cylinder with free-clamp ends. It is under centrifugal load due to its constant rotational speed, uniform internal and external radial loads and arbitrary thermal gradients. The nalysis is initially investigated for the homogeneous state. Then FGM state is investigated to improve the safety factor of the spool. To calculate the safety factor, Von Mises criterion has been used. In FGM state thermoe-lastic properties of material varying in radial direction. The function of these properties’ changes is assumed to be exponential. To obtain the highest safety factor, the numerical opti-mization method has been used and the optimal results have been compared with the homo-geneous state. To drive the relations for free-clamp ends boundary condition, at first spool is considered clamp-clamp ends. Then, the effect of releasing one of the ends has been calculated and finally, using the principle of superposition, the results for clamp-free ends state has been investigated. Also, the effect of changing the non-homogeneous coefficients, spool’s rotating speed, radial loads and thickness on the safety factor are investigated. Increasing the thick-ness and radial loads lead to a change in the optimal coefficient and to reduce the safety factor of optimum state. The results showed that using FGM state with optimal coefficient can signif-icantly increase the safety factor and reduce displacements. Also, increasing the rotation speed and radial loads will result in a change in the optimal non-homogeneous coefficient and reduce its equivalent safety factor.Thu, 25 Apr 2019 19:30:00 +0100Stress Analysis of FGM Rotating Disk Subjected to Mechanical and Thermal Loads in Aircraft Gas ...
http://macs.journals.semnan.ac.ir/article_3787_0.html
According to high usages of rotating disk in aircraft gas turbine engine, turbo pumps in oil and gas industries, steam and gas turbines in power plants, marine gas turbine and other industrial rotary machines designing and getting under the mechanical and thermal loading made this design and analysis to be as a special significance. These disks are subjected to mechanical and thermal loads. In this study, four methods, variable material properties (VMP), Galerkin, Runge-Kutta with two different rules calculate the amount of displacement, stress and strain of a rotary disk which has been used from a functional graded material (FGM). The problem in different states of loading and temperature dependence and independence of the properties has been resolved. Disk properties with the specified function of radius change. Mechanical loading conditions result from the centrifugal disk and blades mounted on it and the effects of shaft pressure and thermal stress caused by temperature difference in the shaft. The results obtained from each of the four methods are closed together and can be used to analyse the problems of this type. By Combining all loads the most radial stresses and environmental stresses respectively obtained in the center of the inner and outer radius and inner radius of the disk. By using the results can get most optimal design of the (FGM) disk.Thu, 25 Apr 2019 19:30:00 +0100Failure Pressure Prediction of Semi Spherical GFRP Shells in Thermal Environment
http://macs.journals.semnan.ac.ir/article_3789_0.html
The pressure tests and temperature effects on the failure of composite pressure vessels is an expensive and time-consuming process. In this research, a new process has been designed in the laboratory scale to manufacture a portion of the composite vessel as a test specimen. The com-posite specimen is manufactured in a close mold and is tested in an apparatus that is able to control gas pressure up to 100 bars and temperature up to 150 Celsius. A spherical cap of com-posite is designed as a test specimen to be pressure tested up to failure at constant temperature. A closed mold has been also designed and fabricated to manufacture the test specimens. Testing apparatus consisting of three-part holder, gas tank, pressure controller and temperature con-troller is designed and fabricated for the failure tests. To examine proper function of the fabri-cated mold and testing apparatus, twelve small spherical cap of the GFRP test specimens manu-factured by the hand layup process considering [0/90/45/-45/90/0] arangment in the fabricat-ed mold. Burn off tests has shown a closed tolerance of fiber volume fraction for all specimens. The test specimens subjected to internal pressure at constant temperature up to failure. A nu-merical analysis of the GFRP spherical cap has been also run using ABAQUS software consider-ing Hashin failure criterion to determine the failure pressure at constant temprature. Both the experimental results and finite element calculation of failure pressure have shown to be close enough to trust the mold and testing apparatus. These results also showed that the failure pres-sure decreases as the temperature increases. The numerical results for prediction of the failure pressure however have shown to be greater than experimental values and an average difference of 16.5% has shown to be all four tests.Thu, 25 Apr 2019 19:30:00 +0100Study on compression and flexural behavior of ABS-SiO2 polymer matrix composite fabricated by ...
http://macs.journals.semnan.ac.ir/article_3790_0.html
In the present manuscript, an experimental study was made to prepare Acrylonitrile- Butadiene-Styrene matrix composite reinforced by Nano-silica particles. Hot extrusion method was utilized here to fabricate the composite specimens used for flexural and compression tests. To identify effect of SiO2 content and extrusion temperature number of 12 experiments has been carried out and the obtained results were discussed according to scanning electron microscopy (SEM) images of the samples cross section. Also, crack propagation and barreling phenomenon was discussed by variation process factors. Obtained results revealed that addition of nano-SiO2 up to 3% causes improvement in both flexural and compression strength while further increase in reinforcement content causes reduction of composite strength. Furthermore, samples which prepared at extrusion temperature of 210º has lower strength compared to those fabricated by 180º temperature. Moreover, it was found that increase in SiO2 content and decrease in extrusion temperature increase the brittleness of composite.Thu, 25 Apr 2019 19:30:00 +0100An Investigation of Stress and Deformation Behavior of Functionally Graded Timoshenko Beams ...
http://macs.journals.semnan.ac.ir/article_3794_0.html
A functionally graded material beam with generalized boundary conditions is considered in the present work to study the deformation and stress behavior under thermal and thermo-mechanical load. Three discrete combinations of functionally graded materials have been con-sidered to include a wide range of materials and material property. The variation of material properties has been taken along the height of the beam cross-section as per power law formula-tion. The formulation has been derived using the principle of virtual work to obtain governing equations for FG Timoshenko beams. The development of governing equations is made using a unique method of unified formulation (Li [16]) in which the displacement variables are arranged in the form of a independent variable that subsequently reduces the equations to a single fourth order differential equation similar to the equation given by classical beam theory and is been extended to thermo-mechanical loading in the present work. The transverse shear stress/ strain for Timoshenko beams have been taken care of within this unified formulation. The for-mulation reported in this work has been generalized for various loading conditions and in the present work thermal and thermo-mechanical load has been considered where temperature has been varied along the beam height. Exact solutions of the fourth order differential equation for the deformation and stress have been obtained for three types of boundary conditions viz.- Clamped-Free (C-F), Simply Supported (S-S) and Propped Cantilever (C-S). The study has been extended to cover wide range of temperature distribution so as to include uniform, linear and non-linear temperature profiles. Deformation and stresses; axial stresses and transverse (shear) stresses, have been reported for different power law index values.Thu, 25 Apr 2019 19:30:00 +0100Vibration analysis of circular single-layer Graphene sheet using Finite Element Method
http://macs.journals.semnan.ac.ir/article_3796_0.html
Graphene sheets are combined of Honeycombs lattice carbon-carbon bonds which have high natural frequencies, high strength, and high conductivity. Due to important applications of the graphene sheets particularly at higher frequencies, the study of their dynamic behavior is important in this frequency range. From Molecular Dynamics (MD) point of view as the dimensions of graphene sheet incline, the number of atoms increases, and as a result, its modeling becomes more time-consuming. Besides the experimental methods in small dimensions are difficult to conduct and not economical. In this research Finite Element Method (FEM) is used for frequency analysis of graphene sheets in various dimensions in order to study the capability of FEM in simulating the dynamic behavior of graphene sheets at small scales. In this research, the objective function is to find the minimum size of the sheet in which both methods have good convergence. Also, the time-consuming for the simulation is investigated. The time-consuming for analysis in the Finite Element Method is less than other methods, including Molecular Dynamics (MD), Generalized Differential Quadrature (GDQ), etc. Also, The results showed that for circular single-layer graphene sheets simulation, using Finite Element Method (FEM) is in good agreement with the results obtained from the Molecular Dynamics (MD) simulation, in the radius more than 100 nm. In this research, the ABAQUS software has been used for simulation by Finite Element Method (FEM).Thu, 25 Apr 2019 19:30:00 +0100A novel method for considering interlayer effects between graphene nanoribbons and elastic ...
http://macs.journals.semnan.ac.ir/article_3891_0.html
A complete investigation on the free vibration of bilayer graphene nanoribbons (BLGNRs) mod-eled as sandwich beams taking into account tensile-compressive and shear effects of van der Waals (vdWs) interactions between adjacent graphene nanoribbons (GNRs) as well as between GNRs and polymer matrix is performed in this research. In this modeling, nanoribbon layers play role of sandwich beam layers and are modeled based upon Euler-Bernoulli theory. To consider effects of vdWs interactions between adjacent GNRs as well as between GNRs and polymer matrix, their equivalent tensile-compressive and shear moduli are considered and utilized in derivation of governing equations instead of employing conventional Winkler and Pasternak effects for elastic medium. The governing equations of motion are derived by considering the assumptions and employing sandwich beam theory, and natural frequencies are obtained by implementing harmonic differential quadrature method (HDQM). A detailed study is performed to examine the influences of the tensile-compressive and shear effects of vdWs interactions between adjacent GNRs as well as between GNRs and polymer matrix on the free vibration of BLGNRs.Sat, 29 Jun 2019 19:30:00 +0100Investigation of Nonlinear Behavior of Composite Bracing Structures with Concrete Columns and ...
http://macs.journals.semnan.ac.ir/article_3953_0.html
The composite structural system (RCS) is a new type of moment frame, which is including a combination of concrete columns (RC) and steel beams (S). These structural systems have the advantages of both concrete and steel frames [1]. In previous research on composite structures, there are some studies regarding RCS composite conections, but there is no investigation about seismic resisting system for these systems in aspect of implementation and performance. In this paper, it is investigated about the seismic behavior of the RCS composite bracing frame. To achieve this objective, nonlinear analysis of RCS composite frames with and without bracing has been done using finite element method. The behavior factors of these frames have been calculated after analyzing frames. It can be seen based on the results of the analysis that braces increase the yielding strength, ultimate strength and stiffness of RCS composite frames. Also, the comparison of analytical and experimental results shows that the nonlinear behavior of RCS can be accurately predicted using finite element method.Sat, 27 Jul 2019 19:30:00 +0100